The signal in the rotation function comes about when the patterson of the probe molecule, Pm, is aligned with the patterson of one molecules from the unit cell, say P1. The noise comes from the overlap of Pm with all the other vectors in the unit cell. If there are N molecules in the unit cell, there are (N-1) self patterson functions misaligned with Pm, and also N(N-1) cross patterson functions (vector sets from molecule i to molecule j) that do not match up with Pm. So the signal to noise goes roughlhy as (1/N*N).
----- Original Message ----- From: Jon Wright <[EMAIL PROTECTED]> Date: Tuesday, January 23, 2007 4:04 am Subject: Re: advice To: [email protected] > Randy J. Read wrote: > > > On Jan 22 2007, Eaton Lattman wrote: > > > >> Will someone knowledgeable tell me what the present state of full 6 > > >> dimensional searches in molecular replacement? > > > > ... > > If the latter, our feeling is that it isn't worth it. We've tried > the > > full search option on a couple of monoclinic problems (where it's > only > > a 5D search), and nothing came up with the full list of orientations > > > that didn't come up with the first hundred or so orientations. ... > > As a related question, can anyone comment on the effects of symmetry > on > MR (or direct me to appropriate literature)? Seems the rotation > function should give less information as the number of symmetry > related > copies of the molecule in the unit cell goes up. Do people take into > account space group when deciding how many translation functions to > compute? > > Thanks, > > Jon
begin:vcard n:LATTMAN;EATON fn:EATON E LATTMAN tel;work:410 516 8215 org:Johns Hopkins University;Biophysics adr:;;Mergenthaler 237;Baltimore;MD;21218; version:2.1 email;internet:[EMAIL PROTECTED] title:Dean of Research, Professor of Biophysics end:vcard
